Embodiments of the invention generally relate to devices and processes for forming the same. More specifically, embodiments of the invention are directed to backside illuminated image sensors with a tunable electrostatic effect and methods of forming the same.
In the formation of a backside illuminated (BSI) CMOS image sensors (CIS), a dielectric film is deposited above the photodiode. This dielectric film, frequently made of hafnium oxide, often has fixed negative charges to create a hole accumulation layer to suppress dark current caused by the interface between the photodiode and the dielectric layer. However, the electrostatic effect of the interface is not eliminated.
There is a need to control the electrostatic charge for many applications, including charges that result in dark current for optical applications. Typically, this is done by using hafnium oxide only films, and changing the thickness or implant conditions of the fixed negative charge inducing species.
However, there remains a need in the art for methods to provide control the electrostatic effect for a given film thickness.